5. Cell Structure And Organization - part 14 - Cytoskeleton

 

5. Cell Structure And Organization - part 14 - Cytoskeleton


Cytoskeleton :

  • With advancement in light and electron microscopy, scientists revealed presence of network of fibrils throughout the cytoplasm. It is called cytoskeleton. 
  • Cytoskeleton consists of - 
  1. microtubules
  2. microfilaments and
  3. intermediate filaments. 
1. Microtubules :-  are made up of protein- tubulin.
2. Microfilaments :-  are made up of actin and intermediate filaments are composed of fibrous proteins.


  • Cytoskeleton helps in - 
  1. maintenance of shape of cell
  2. contraction of cell
  3. mobility of cell and cell organelles
  4. changes in shape of the cells and cell division.

Cilia and flagella :


  • They are fine hair like membrane bound protoplasmic outgrowths that occur on the free surface of the cell. 
  • They generate a current in fluid medium for passage of material and locomotion. 
  • Cilia are small in size and many in number. 
  • Cilia act as oars causing movement of cell. 
  • Flagella are longer and few in number. 
  • Flagella present in prokaryotic bacteria are structurally different from that of eukaryotic flagella. 
  • Cilium or flagellum consists of - 
  1. basal body
  2. basal plate and 
  3. shaft.


  • Basal body is placed in outer part of cytoplasm. It is derived from centriole. It has nine peripheral triplets of fibrils. 
  • Shaft is exposed part of cilia or flagella. It consists of two parts- sheath and axoneme. 
  • Sheath is covering membrane of cilium or flagellum.
  • Core called axoneme possesses 11 fibrils running parallel to long axis. 
  • It shows 9 peripheral doublets and two single central fibrils (9+2). 
  • The central tubules are enclosed by central sheath. This sheath is connected to one of the tubules of peripheral doublets by a radial spoke.
  • Central tubules are connected to each other by bridges. 
  • The peripheral doublets are connected to each other through linkers or interdoublet bridge.

Centrioles and centrosomes :


  • Centrosome is usually found near the nucleus of an animal cell. 
  • It contains a pair of cylindrical structures called centrioles.
  • The cylinders are perpendicular to each other and are surrounded by amorphous substance called pericentriolar material. 
  • Each cylinder of centriole is made up of nine sets of triplet microtubules made up of tubulin. 
  • Evenly spaced triplets are connected to each other by means of non-tubulin proteins.
  • At the proximal end of centriole, there is a set of tubules called hub. 
  • The peripheral triplets are connected to hub by means of radial spokes. 
  • Due to this proximal end of centriole looks like a cartwheel. 
  • The centrosomes help in assembly of spindle apparatus during cell division. 
  • It forms basal body of cilia and flagella.



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